Electrical socket connection

[Richardtr3a]

I need some help from an electrical expert please.

 

I need to connect a socket for the sat nav. My car is still +earth so I have to be careful.

 

I will connect the socket pin to my earth and the socket body to a supply. Which would be the best connection point? I will also fit an in line fuse. What rating should it have?

 

I hope that I am doing this the right way. Any advice would be very helpful.

 

Thanks Richard & H.

 

 

[RobH]

Your proposal is correct Richard. Fuse no greater than 5 Amps. You can connect to the A1 terminal on the fuse-box if you want the feed 'live' all the time, or to the A3 terminal if you want it to switch on and off with the ignition.

 

It would be safer to swap the car's polarity but a low-value fuse should prevent disaster for the wiring loom if you do get a short - though the sat-nav or charger might not survive. If there is a charger lead to the sat-nav which has a metal ring on the outside of the connector, remember that will be at battery live and should not be allowed to touch any metal part of the car when disconnected from the sat-nav.

 

Rob

[Richardtr3a]

Thanks Rob.,

 

I am going to cut off the existing plug and that should eliminate that problem.

[foster461]

Your proposal is correct Richard. Fuse no greater than 5 Amps. You can connect to the A1 terminal on the fuse-box if you want the feed 'live' all the time, or to the A3 terminal if you want it to switch on and off with the ignition.

 

It would be safer to swap the car's polarity but a low-value fuse should prevent disaster for the wiring loom if you do get a short - though the sat-nav or charger might not survive. If there is a charger lead to the sat-nav which has a metal ring on the outside of the connector, remember that will be at battery live and should not be allowed to touch any metal part of the car when disconnected from the sat-nav.

 

Rob

 

That is an excellent point Rob and one that I had not considered. We often see warnings about devices with metal cases but even with all plastic devices the metal tip of the connector may be a problem. I just tested with a USB cable and sure enough when the cable is unplugged from the device the outer metal contact of the connector will short against anything grounded like the handbrake lever or the grab handle.

 

That tells me I need to be careful to plug the cable into the device before plugging the other end into the USB power socket.

 

Stan

[harrytr5]

Forgive me for intruding, but it is so easy to swap polarity. I did this on a friends TR3a and his satnav ,LED rear lights and all sorts of stuff that the modern Negative earth works under.Much better than having the shell live so to speak.

Regards Harry

[Lebro]

I too would recommend changing to -ve earth.

 

Bob.

[McMuttley]

OK Gents

 

I was about to take the lighter socket connector off in order to hard wire in, but....

 

When I took the plug apart, I expected to see a red and a black wire, but both appear to be black ????

 

Does it matter which I use as power / ground ?

 

If it does, would ground be the 'nipple' at the front and power the side springs, or visa versa ?

 

In case it makes a difference, the wire to the springs is a tick gauge coper core, whereas the wire to the 'nipple' is much thinner, but appears to be in another wire sleeve to equal up the thickness ?????

 

 

Edited July 6, 2016 by McMuttley

[peejay4A]

The centre pin is positive. Although both are black it's common for the positive to have a raised "edge" moulded into the sheath so as to distinguish it from the other conductor. It's possible that your device has a bridge rectifier on the power input to make it polarity independent but I wouldn't risk it.

Edited July 6, 2016 by peejay4A

[RobH]

Looks to me as though your thin positive wire has a joint in it alongside the one which connects to the spring. Odds-on the main twin flex has both cores the same thickness Austin. Polarity is important particularly since your new socket has a USB connector in it - and hence a regulator 'chip' - which will definitely be unhappy if you get it the wrong way round. I suggest you mark the positive core somehow before you cut the original connections off - red sticky tape is good.

[Lebro]

The positive side of the twin black wire is usually marked with 3 or so raised lines running along it's length.

But check it with a meter first.

Positive to centre pin, -ve to side.

 

Bob.

[McMuttley]

Thanks Bob, n all

 

No clues or ridges on backed, just the odd double layer on the (assumed) -'ve

 

 

OK, so I have found what I assume is a multimeter !

 

To what position do I turn the dial and what should I expect it to do if I follow the red/nipple, black spring or visa versa.

 

In most cases nowt happened, although on the V left side at 2000m, if i did it the red/nipple side it flickered up to +3 or visa versa -4 ????

[peejay4A]

I can't follow where you're connecting the meter Mac.

[Lebro]

You should have it on the V left side at "20" that means it will measure DC voltage up to 20 Volts.

You should see 12V or there abouts. Your result suggests that you have no voltage on there at all.

 

I may be confused about what you are trying to measure.

If you just want to get rid of the plug, then remove the wire which goes to the centre pin, & connect to +ve 12V

& the other (outside connection) to ground.

This assumes -ve earth.

 

Bob.

Edited July 6, 2016 by Lebro

[RobH]

What are you trying to check Austin?

 

The wire to the 'nipple' is the positive connection and the one to the 'spring' is the negative. Without any connection of the socket to a supply the meter shouldn't really read anything on the Volts range. (though if you have had the socket plugged in there might be some stray charge left)

 

The only thing you can check with the socket disconnected is the continuity between the nipple and the centre of the socket , or the spring and the outer of the socket. I'm not sure that is going to help any as it will just confirm what we already know.

 

Switch you meter to the diode position (the little triangle sign with the curved lines just to the right of the 200 position at the bottom). When you touch the meter leads together you should hear a bleep showing that there is a connection. You can use that to trace wires provided there is no power on them.

 

When you have your socket wired in, switch the meter to DC Volts and the 20 volt range - that is the position on the left just above the 2000m one, and is the position to be used for all voltage measurements on your car. With the power on, put the red lead on the centre pin of the lighter socket and the black one on the outer sleeve. If you have it connected correctly you should see a positive reading of about +13 volts .

[peejay4A]

On where?